Terrorist attacks in eastern Ethiopia this week have drawn attention to the plight of ethnic Somalis living in Ethiopia's Ogaden region, where opposition groups have accused Ethiopia's government of massive human rights abuses over the last decade, including hundreds of killings and disappearances.

So far, no one has claimed responsibility for a series of grenade attacks that killed five people and injured 31 others Sunday in the eastern Ethiopian town of Jijiga.

Authorities there say the violence was politically motivated, coming just two weeks before voters in the region cast their ballots in Ethiopia's parliamentary election, in which most of the country voted in May.

But the killings have focused international attention on the plight of those living in Ogaden, an arid region roughly the size of Britain. Most of the four million people are Somalis. The region is important seasonal grazing land for cattle, goats and camels migrating from Somalia.

In the late 1970s, Somalia and Ethiopia went to war over Ogaden. Somalia claimed Ogaden belonged to it and that the colonial boundaries ignored centuries-old migration patterns of Somalis into what is now part of Ethiopia.

Somalia lost the war, but that didn't restore calm in Ogaden. There are several Ethiopian opposition groups operating in the area, including the Ogaden National Liberation Front, or ONLF. Another group, al-Ittihad, an Islamist organization linked to al-Qaida, according to experts, has petered out over the last decade.

Matt Bryden, Horn of Africa director for the International Crisis Group, says the ONLF might have its share of grievances with Ethiopia's government, but it was unlikely behind the attack.

"The ONLF has been fighting for a number of years for self-determination of the Somali people within Ethiopia," he said. "They have operated mainly far to the southeast of Jijiga, and their attacks have, for the most part, focused on Ethiopian armed forces, and occasionally ambushes on civilian trucks and humanitarian personnel."

Ogaden has seen an increase of activity in recent months. The United States military is conducting training exercises in the region as part of the U.S.-led war on terror in the Horn of Africa.

Also, the Malaysian oil company, Petronas, just sealed a four-year deal with Ethiopia's government to explore for oil in the Ogaden region. The deal angered ONLF leaders, who vowed to block the government's attempts to profit from Ogaden's potential oil wealth.

Still, Mr. Bryden says he doubts the oil deal is linked to the recent violence.

"I would be surprised simply because there would be no point for the ONLF to throw grenades into bars in Jijiga," he said. "They would be much more likely to make their displeasure known in the area where the drilling is supposed to take place. So, at the moment I'd say it's too early to draw a link between the two."

Meanwhile, people in the Ogaden region are preparing for the August 15 elections to fill 23 seats in Ethiopia's 547-member parliament. Several opposition groups, already claiming massive voting fraud, have recently staged violent protests in the capital, Addis Ababa.